Diffusion-limited reactions in dynamic heterogeneous media

Abstract

Most biochemical reactions in living cells rely on diffusive search for target molecules or regions in a heterogeneous overcrowded cytoplasmic medium. Rapid re-arrangements of the medium constantly change the effective diffusivity felt locally by a diffusing particle and thus impact the distribution of the first-passage time to a reaction event. Here, we investigate the effect of these dynamic spatio-temporal heterogeneities onto diffusion-limited reactions. We describe a general mathematical framework to translate many results for ordinary homogeneous Brownian motion to heterogeneous diffusion. In particular, we derive the probability density of the first-passage time to a reaction event and show how the dynamic disorder broadens the distribution and increases the likelihood of both short and long trajectories to reactive targets. While the disorder slows down reaction kinetics on average, its dynamic character is beneficial for a faster search and realization of an individual reaction event triggered by a single molecule.

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• Random coefficient autoregressive processes describe Brownian yet non-Gaussian diffusion in heterogeneous systems
• Codifference can detect ergodicity breaking and non-Gaussianity
• Reversible reactions controlled by surface diffusion on a sphere
• First passage time for superstatistical Fokker-Planck models